What is headrail allowance?
Headrail allowance is the extra length we allow in the top section of the blind to cover the batten/rail and give room for the rod pockets, rings and eyelets on a wooden batten when the blind is pulled up. In our tutorials we suggest an absolute minimum headrail allowance of:
Traditional batten: HEADRAIL ALLOWANCE = Batten face + 3.5cm Headrail mechanisim: HEADRAIL ALLOWANCE = Headrail depth + 2.5cm
The traditional wooden batten on the left has a face depth of 3cm and the minimum distance needed below the blind is 3.5cm. Note if you are using larger eyelets you may need more than 3.5cm below the batten. That gives an absolute minimum headrail allowance of 6.5cm.
The headrail on the right has a depth of 3cm and the minimum distance needed below the blind is 2.5cm, giving an absolute minimum headrail allowance of 5.5cm.
(Note the stitch line of the rod pocket marks the top of the blind fold.)
In this next example the headrail depth is 4cm and you can see the minimum needed below the headrail is 2.5cm, giving an absolute minimum headrail allowance of 6.5cm.
What if I make my headrail allowance to short?
The headrail allowance has to be sufficiently long to cover the face of the batten and allow room for the pleats to pull up so the blind can be pulled fully up.
If you do not allow enough headrail allowance the blind will not fully pull up. You can see here the headrail allowance used is too short because even though the rings are pulled up tight to the headrail the blind is still hanging down slightly.
What if I use a headrail allowance longer than the minimum?
If you use a headrail allowance longer than the minimum the blind will still work fine. Indeed we don’t usually use the absolute minimum, finding it is better to not be up against the limit. You can see the rings just hang slightly lower when the blind is up with the pleats aligned.